[Source Generator] Source Generator works with dotnet cli but fails with `TypeLoadException` in VS

[LittleLittleCloud]

Description

The source generator can successfully generate source code when I compile using dotnet cli. It also successfully generates source code in VS UI when I expand the analyzer node. But it raises a TypeLoadException when I compile and run my code in VS by hitting control + F5.

Here is the link to the source code of source generator: https://github.com/tryAGI/AutoSDK/tree/main/src/libs/AutoSDK.SourceGenerators

Here is the dotnet --list-sdks

8.0.400 [C:\Program Files\dotnet\sdk]
9.0.100-preview.7.24407.12 [C:\Program Files\dotnet\sdk]

Here is the error log in VS:

Build started at 9:24 AM...
1>------ Build started: Project: SourceGen, Configuration: Debug Any CPU ------
1>CSC : warning CS8784: Generator 'SdkGenerator' failed to initialize. It will not contribute to the output and compilation errors may occur as a result. Exception was of type 'TypeLoadException' with message 'Could not load type 'AutoSDK.Models.ModelData' from assembly 'AutoSDK, Version=0.0.0.0, Culture=neutral, PublicKeyToken=603f13207e65c17b'.'.
1>SourceGen -> C:\Users\xiaoyuz\source\repos\SourceGen\bin\Debug\net8.0\SourceGen.dll
1>Done building project "SourceGen.csproj".

Here is the screenshot of which VS I am using:

Finally, the link to a minimal reproducable example for this bug.

• https://github.com/LittleLittleCloud/ItRaiseTypeLoadedExceptionFomSourceGenerator

Reproduction Steps

See above

Expected behavior

Source generator successfully generate source in VS

Actual behavior

It raise a TypeLoadException

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response

[huoyaoyuan]

Questions for source generator belong to roslyn repo.
Source generators must target netstandard2.0 since VS is still on netfx. It's expected to fail if you target net8.0. See dotnet/roslyn#72777

[LittleLittleCloud]

@huoyaoyuan Thanks for reply, I can transfer this issue to roslyn repo.

Curious to ask though, why the behavior is different when using source generator in dotnet cli versus using in VS. In the example above, the source generator can successfully generate code when I compile from command line using dotnet cli.

[huoyaoyuan]

Dotnet cli executes almost everything with the same .NET version of the SDK, while VS executes roslyn with .NET Framework because itself is still on .NET Framework.

Source generators or analyzers should target the exact same lowest framework version of roslyn, to ensure any process that's capable loading roslyn can load the analyzer/generator. It also should reference the lowest roslyn version it need to support.

[jeffschwMSFT]

@jaredpar can you help with the transfer to roslyn?

[jaredpar]

Analyzers and generators are plugins to the compiler and they need to operate wherever the compiler operates. That includes running on .NET Framework and NET Core (potentially multiple versions). That is why they are strongly recommended to target netstandard2.0. When you target net8.0 it's expected that you will fail in cases where the compiler runs on .NET Framework

[LittleLittleCloud]

@jaredpar Thanks for the explanation, can I understand it in the way that if my project targets to net 8.0 and source generator targets to netstandard 2.0, it's expected that the source generation might fail in Visual Studio if the source generator uses any API that is net 8.0 only?

[jaredpar]

it's expected that the source generation might fail in Visual Studio if the source generator uses any API that is net 8.0 only?

Correct. It will fail for any API that is net8.0.

[HavenDV]

This source generator does not use any net8.0 apis. It's usual netstandard2.0 source generator which uses netstandard 2.0 library inside.

The only possible problem I see is some duplicate files inside the analyzers directory:

P.S. Removed in latest dev version

[huoyaoyuan]

This source generator does not use any net8.0 apis.

The original message hints that its dependency (AutoSDK) attempts to load net8.0 api.

[HavenDV]

I don't see anything meaningful in the message except the version number. Another idea is that it might have something to do with using MinVer, there was a recent update to version 6.0.0 that might have broken something.